The research proposed is focused on physiological interactions between mammals and microorganisms indigenous to their gastro-intestinal tracts. Germfree, gnotobiotic and specific pathogen-free mice and rats are used; certain microbes that associate intimately with mucosal epithelia receive special emphasis. Our long-term goals are to learn how these microbes remain and proliferate in their habitats and how they influence certain physiological responses in their mammalian hosts. In seeking the first goal, we examine the mechanisms by which microbes adhere to and grow on the epithelia. Microbial culture techniques including methods for culturing oxygen-intolerant anaerobic bacteria, frozen-section histology, and transmission and scanning electron microscopy are used to characterize the associations. Surface components of the microbial cells are isolated, purified and assayed in systems designed to detect their function in the adherence activity. In seeking the second goal, we examine the mechanisms by which certain of the microbes depress the activity levels of enzymes such as phosphatases and disaccharidases in the microvillous membranes of cells of the intestinal epithelium of mice. Microbial culture and biochemical techniques including spectrophotometry, column chromatography, and polyacrylamide gel electrophoresis are used in characterizing the enzymes in the intestinal epithelia. Germfree mice, both pen-bred and inbred, are monoassociated with indigenous microbes that attach to epithelial surfaces. These gnotobiotics are used in experiments designed to determine whether or not the microbes depress the activity levels of the phosphatases by altering the migration rate of intestinal epithelial cells. Liquid scintillation counting is used in assays of the rates of migration of the cells.